1. Field of the Invention
This invention relates to a process for disproportionation of toluene utilizing a phosphorus-containing crystalline aluminosilicate zeolite catalyst to yield benzene and xylenes in which the proportion of para-xylene isomer is substantially in excess of its normal equilibrium concentration.
2. Description of the Prior Art
The disproportionation of aromatic hydrocarbons in the presence of ziolite catalysts has been described by Grandio et al. in the Oil and Gas Journal, Vol. 69, Number 48 (1971).
U.S. Pat. Nos. 3,126,422; 3,413,374; 3,598,878; 3,598,879 and 3,607,961 show vapor-phase disproportionation ot toluene over various catalysts.
In these prior art processes, the xylene product produced has the equilibrium composition of approximately 24 percent of para, 54 percent of meta and 22 percent of ortho. Of the xylene isomers, i.e. ortho-, meta- and para-xylene, meta-xylene is the least desired product, with ortho- and para-xylene being the more desired products. Para-xylene is of particular value being useful in the manufacture of terephthalic acid which is an intermediate in the manufacture of synthetic fibers such as "Dacron". Mixtures of xylene isomers either alone or in further admixture with ethylbenzene have previously been separated by expensive superfractionation and multistage refrigeration steps. Such process, as will be realized, has involved high operation costs and has a limited yield.